Switch will take another 3 to 6 days, during which oil will flow unimpeded

New Orleans, Louisiana (CNN) -- BP said Sunday that it is "pleased" with how the operation to place a new cap on its ruptured undersea well is proceeding.

Officials hope the containment cap will stop oil from gushing into the Gulf. But while robots replace the old cap, crude is flowing freely.

The procedure -- expected to take four to seven days -- continued to progress Sunday as crews worked to position a transition spool over the gushing well to prepare for the new connection, according to BP's Senior Vice President Kent Wells.

"We're pleased with how it's going," Wells said, but cautioned that the operation, which began Saturday with the removal of the old cap, is only in its second day.

Robots removed six giant bolts from the apparatus early Sunday so that the new cap could be positioned.

If successful, the effects of the containment cap operation could halt the oil gusher that started April 20 after a deadly explosion on the Deepwater Horizon rig in the Gulf of Mexico.

But officials have said the new containment cap would be a temporary fix, and the permanent solution would still be completion of a relief well. There are two relief wells under construction.

Wells said Sunday that one of the relief wells could intercept the ruptured well as early as the end of July.

"We're feeling very good about how we've positioned that well," he said.

The other relief well is expected to be completed in August.

The old cap had been diverting about 15,000 barrels a day (630,000 gallons) to a ship. BP still is recovering an additional 8,000 to 9,000 barrels a day (336,000 to 378,000 gallons) through a line connected to another vessel, the Q4000.

"As we start to ramp up the additional containment capacity, we should see less and less flow," Wells said.

The Helix Producer recovery vessel is expected to begin collecting oil Sunday evening, Wells said, and officials hope to reach its full collection capacity of 20,000 to 25,000 barrels (840,000 to 1.5 million gallons) per day within three days.

Over the next two to three weeks, 60,000 to 80,000 barrels (2.52 million to 3.36 million gallons) a day should be collected as part of the containment process, Wells said. Scientists estimate that 35,000 to 60,000 barrels of oil are spewing daily from BP's breached well.

BP says there will be a period of decreased oil and gas capture from the wellhead during the cap replacement. It said another recovery vessel, the Q4000, "should continue to capture and flare oil and gas." There will be other recovery vessels and skimmers deployed.

Two more oil skimmers were added to the Gulf Sunday bringing the total to 48 collecting an oil and water mix from the surface, BP officials said. And another 15 burns were conducted in calm seas.

"It was a good day in trying to contain the oil that made it out to the surface," Wells said.

Wells also said there will be "significant measurement capability" added to the new cap so officials can get a good idea of the flow rate.

BP said in a statement that the new cap "should improve containment efficiency during hurricane season by allowing shorter disconnect and reconnect times."

Retired Coast Guard Adm. Thad Allen said Friday that the new cap would allow responders to collect more accurate oil flow data and that, once the switch is complete, the resulting capacity to contain oil "will be far greater than the capabilities we have achieved using current systems."